Due to limitations inherent in the rocket manufacturing process, among other reasons, the thrust vector of a rocket can never be perfectly aligned with the longitudinal axis of the rocket. This results in a thrust misalignment that generates asymmetrical forces on the rocket causing unwanted pitch and yaw attitude changes which have adverse effects on the flight trajectory and decrease the probability of target interception.
A solution to this problem is to impart a spin to the rocket motor during the boost phase which mitigates the effect of these asymmetrical forces and other lateral body movements. The spin may be imparted by fluting at the base of the rocket motor which converts some of the downward thrust to rotational torque.
Some guidance strategies require the rocket to be de-spun, before guidance initiation starts at about the time that the rocket motor burns out. The process for de-spinning the rocket is called autopilot roll capture and it is typically initiated at a fixed time after launch to insure the process is completed at a later fixed time to handle the worst case scenario (longest de-spin time) which occurs at high altitudes and low speeds.
Unfortunately, at lower altitudes and/or launches from high speed platforms, the de-spin process completes in a shorter period of time due to the greater aerodynamic forces which results in a de-spun rocket while the rocket motor is still providing thrust. Rocket motor thrust misalignment in this situation can severely impact the rocket trajectory and decrease the probability of intercept.
What is needed, therefore, are techniques for adaptively controlling the roll capture process so that the rocket is de-spun at the optimal time.